Hyperbranched refers to a class of very highly branched polymers which tend to be globular in form. Various types of hyperbranched polymers, which are represented by the Starburst.TM. dendrimers (treelike polymers), are known. These hyperbranched polymers have higher functional group densities per molecular unit than straight-chain polymers and conventional branched polymers. Another characteristic feature of the hyperbranched polymers is that they possess an internal space once they have been elaborated to several generations. These characteristics point to potential applications as surfactants, gelling agents, drug delivery systems, polymeric absorbents, and the like.
Additionally, introduction of the siloxane bond into the hyperbranched polymer format could provide a hyperbranched polymer that possesses the unique features of polysiloxanes. Various polysiloxane-based hyperbranched polymers have already been proposed. Hyperbranched siloxane polymers can have a SiH surface or an alkenyl or alkynyl surface. However, it is difficult to prepare hyperbranched polymers with a SiH surface because of several factors, including the instability of the SiH precursors, difficulty in controlling the reaction to prevent crosslinking, and difficulty in preventing side reactions during storage. For example, JP-A 03-263,431 teaches a method for synthesizing a SiH-functional polysiloxane dendrimer by repeating a multi-step reaction that includes condensation of the SiCl and SiOH groups and hydrolysis of the SiH group. This method, however, is unsuitable for large-scale industrial production due to its complex synthetic procedure and low overall yield.
In Organometallic News, 40-42 (1993), a method is proposed for the synthesis of a SiH-functional polysiloxane dendrimer by reacting polyfunctional chlorosilane with 1,1,3,3-tetramethyldisiloxane in the presence of hydrochloric acid to replace the chlorine atom of SiCl with the dimethylsiloxy group. Since these synthetic methods are each multi-step reactions with isolation and purification at each step, they offer the advantage of producing dendrimers with defined structures and narrow molecular weight distributions. However, they require repetition of the reaction process a number of times in order to obtain dendrimer of the desired generation and they have low overall yields, and these features make them very unsuitable for large-scale industrial production.
Hyperbranched poly(siloxysilanes) are described by Mathias and Carothers in J. Am. Chem. Soc. 1991, 113, 4043-4044. A monomer of the formula Vi(CH.sub.2)Si(OSiMe.sub.2 H).sub.3, where Vi is vinyl and Me is methyl, is polymerized using a platinum hydrosilation catalyst. The resulting hyperbranched polymer with a SiH surface can be stabilized by capping with allylphenylether.
In contrast, in J. Inorg. Organomet. Polym. 4(1), 61-77 (1994) a single-step method is proposed for obtaining SiH-functional or Si-vinyl-functional hyperbranched polysiloxane by the intermolecular hydrosilylation reaction of vinyltris(dimethylsiloxy)silane or tris(vinyldimethylsiloxy)silane. While this method cannot provide a narrow molecular weight distribution or defined-structure dendrimer, it nevertheless offers the advantage of providing a Si-functionalized hyperbranched polysiloxane in a single step and has the potential for large-scale industrial production.
Due to the close proximity of the silicon-bonded hydrogen and vinyl in this method, steric hindrance increases in association with the development of the hydrosilylation reaction to such a degree that bringing the reaction to completion becomes quite problematic. In addition, this method has been unable to bring the properties characteristic of polysiloxanes to the hyperbranched polymer format because it gives polymer that has the silethylenesiloxane structure.
As a consequence, a highly reactive, SiH-functional polysiloxane that can provide SiH-functional hyperbranched polysiloxane in a single step is desired. Specifically, an object of the present invention is to provide an organopolysiloxane macromonomer and a method for its preparation. The macromonomer carries an aliphatically unsaturated organic group at one molecular chain terminal and silicon bonded hydrogen atoms at the other terminal. A further object of the invention is to provide a hyperbranched polymer by polymerizing the macromonomer. A further object of this invention is to provide a method for stabilizing the monomer.